Electrochemical energy cell system

ABSTRACT

A metal halogen electrochemical energy cell system that generates an electrical potential. One embodiment of the system includes at least one cell including at least one positive electrode and at least one negative electrode, at least one electrolyte, a mixing venturi that mixes the electrolyte with a halogen reactant, and a circulation pump that conveys the electrolyte mixed with the halogen reactant through the positive electrode and across the metal electrode. Preferably, the negative electrodes are made of zinc, the metal is zinc, the positive electrodes are made of porous carbonaceous material, the halogen is chlorine, the electrolyte is an aqueous zinc-chloride electrolyte, and the halogen reactant is a chlorine reactant. Also, variations of the system and a method of operation for the systems.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to metal halogen electrochemical energy systems.

2. Related Art

One type of electrochemical energy system uses a halogen component for reduction at a normally positive electrode, and an oxidizable metal adapted to become oxidized at a normally negative electrode during the normal dispatch of the electrochemical system. An aqueous electrolyte is used to replenish the supply of halogen component as it becomes reduced at the positive electrode. The electrolyte contains the dissolved ions of the oxidized metal and reduced halogen and is circulated between the electrode area and a reservoir area and an elemental halogen injection and mixing area, to be consumed at the positive electrode. One example of such a system uses zinc and chlorine system.

Such electrochemical energy systems are described in prior patents including U.S. Pat. Nos. 3,713,888, 3,993,502, 4,001,036, 4,072,540, 4,146,680, and 4,414,292. Such systems are also described in EPRI Report EM-1051 (Parts 1-3) dated April 1979, published by the Electric Power Research Institute. The specific teachings of the aforementioned cited references are incorporated herein by reference.

SUMMARY OF THE INVENTION

There are certain weaknesses or disadvantages in prior electrochemical energy systems for standby applications. These include, but are not limited to, the following:

-   -   an inability to store sufficient energy without requirement to         charge the system, precluding availability while in a discharged         condition;     -   complexity and inefficiency of requiring active cooling systems         during discharge, which can further reduce capacity;     -   ambiguities in diagnosing symptoms of failure, which can         significantly increase a probability of failure; and     -   hydrogen generation, which can be a significant and costly         safety issue.

Specific weaknesses or disadvantages in prior metal halogen systems for standby applications also include, but are not limited to, the following:

-   -   inability to maintain a state of readiness without significant         capacity loss due to self-discharge;     -   mal-distribution of zinc metal from internal shunt currents         between cells of differing potential further reduces available         capacity;     -   a long length of small diameter channels required for minimizing         shunt currents during operation further reduce system capacity         due to pumping losses;     -   metallic dendritic growth during the charge mode can permanently         damage a metal halogen system and lead to premature and         hazardous failure conditions.

The invention attempts to address some or all of these weaknesses and disadvantages. The invention is not limited to embodiments that do, in fact, address these weaknesses and disadvantages.

Some embodiments of the invention that attempts to address some or all of these weaknesses and disadvantages are metal halogen electrochemical energy cell systems. These embodiments preferably include at least at least one positive and at least one negative electrode, a reaction zone between the positive electrode and the negative electrode, at least one electrolyte that includes a metal and a halogen, and a circulation pump that conveys the electrolyte through the reaction zone, wherein the electrolyte and a halogen reactant are mixed before, at, or after the pump. Preferably, the positive electrode is made of porous carbonaceous material, the negative electrode is made of zinc, the metal include zinc, the halogen includes chlorine, the electrolyte includes an aqueous zinc-chloride electrolyte, and the halogen reactant includes a chlorine reactant. One effect of this arrangement is generation of an electrical potential.

A preferred embodiment further includes a mixing venture that mixes the electrolyte and the halogen reactant, as well as a metering valve or positive displacement pump that controls flow of the halogen reactant to the mixing venturi.

A flow of the electrolyte preferably undergoes concurrent first, second, and third order binary splits before being conveyed through the reaction zone, thereby providing a same flow resistance for different paths to the reaction zone.

Preferred embodiments of the systems also include a reservoir from which the electrolyte is conveyed by the circulation pump to the cell and to which the electrolyte returns from the cell, an upward-flowing electrolyte return manifold to facilitate purging of gas from the cell, and a return pipe through which the electrolyte returns from the cell to the reservoir.

The halogen reactant preferably is supplied from an external source and preferably is supplied under pressure. In this context, “external” refers to external to the system. An enthalpy of expansion of the halogen from the external source tends to act to cool the system. Alternatively, the halogen reactant can be supplied from a source internal to the system.

The systems preferably include plural such cells, each of which is horizontal and plural of which are stacked vertically in the system. Vertical steps in cell geometry tend to result in interrupted electrolyte flow paths within each of the plural cells, thereby interrupting shunt currents that otherwise would continue to occur after electrolyte flow stops.

The plural cells preferably include plural cell frames. The cell frames can be circular to facilitate insertion of the plural cells into a pressure containment vessel. The preferred form of the cell frames each include a feed manifold element, distribution channels, flow splitting nodes, spacer ledges, flow merging nodes, collection channels, and a return manifold element. When cell frames having this form are stacked, these structures form additional structures within the system. In particular:

-   -   the feed manifold element in each of the plural cells frames         aligns with the feed manifold element in another of the cell         frames, thereby forming a feed manifold;     -   the distribution channels and the flow splitting nodes in each         of the cell frames align with the distribution channels and the         flow splitting nodes in another of the cell frames, thereby         forming a distribution zone;     -   the positive electrode for each cell sits above or below the         negative electrode for each cell on the spaces ledges of the         cell frames, thereby forming alternating layers of positive         electrodes and negative electrodes;     -   the flow merging nodes and the collection channels in each of         the plural cells frames align with the flow merging nodes and         the collection channels in another of the cell frames, thereby         forming a collection zone; and     -   the return manifold element in each of the cell frames aligns         with the return manifold element in another of the cell frames,         thereby forming a return manifold.

The cell frames can include bypass conduit elements for fluid flow and electrical wires or cables and preferably provide a pass-through for an alignment and clamping element to align and to hold the cell frames together.

The invention is not limited to systems with cells that include cell frames.

Whether or not cell frames are used, preferred embodiments of the systems include a feed manifold and a distribution zone for the electrolyte to the plural cells, and a collection zone and a return manifold for the electrolyte from the plural cells. The positive electrode and the negative electrode in each cell preferably are arranged to maintain contact with a pool of electrolyte in each cell when electrolyte flow stops and the feed manifold, distribution zone, collection zone, and return manifold drain.

In some embodiments, a balancing voltage can be applied to inhibit electrochemical reactions and thereby maintain system availability when the system is in a standby or stasis mode. A blocking diode also can be applied to output terminals of the system to inhibit reverse current flow within the system.

The basic operation of preferred embodiment of the system is as follows: aqueous electrolyte is sucked up from a reservoir and through a mixing venturi where halogen such as elemental chlorine is metered into an electrolyte. The halogen mixes with and dissolves into the electrolyte while its latent heat of liquefaction also cools the mixture. The cooled and halogenated aqueous electrolyte passes through the pump and is delivered to positive electrodes in a stack assembly. The positive electrodes preferably are made of porous carbonaceous material such as porous graphite-chlorine. The electrolyte passes through the positive electrodes, reducing the dissolved halogen. The halogen-ion rich electrolyte then passes by one or more a negative electrode preferably made of a metal such as zinc, where electrode dissolution occurs. These reactions yield power from the electrode stack terminals and metal-halogen is formed in the electrolyte by reaction of the metal and the halogen.

The invention also encompasses processes performed by embodiments of the metal halogen electrochemical energy cell system according to the invention, as well as other systems and processes.

This brief summary has been provided so that the nature of the invention may be understood quickly. Other objects, features, and advantages of the invention will become apparent from the description herein, from the drawings, which show a preferred embodiment, and from the appended claims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a metal halogen electrochemical energy cell system according to the invention.

FIG. 2 illustrates flow paths of an electrolyte through the cell plates of an embodiment of the system illustrated in FIG. 1.

FIG. 3 illustrates cell frames that can be used in the system illustrated in FIGS. 1 and 2.

DETAILED DESCRIPTION OF THE INVENTION Electrolyte Energy Cell System

FIG. 1 illustrates a metal halogen electrochemical energy cell system according to the invention.

One embodiment of the invention that attempts to address some or all of these weaknesses and disadvantages is a metal halogen electrochemical energy cell system. This embodiment includes at least at least one positive and at least one negative electrode, a reaction zone between the positive electrode and the negative electrode, at least one electrolyte that includes a metal and a halogen, and a circulation pump that conveys the electrolyte through the reaction zone. The electrolyte and a halogen reactant can be mixed before, at, or after the pump, for example using a mixing venture. Preferably, the positive electrode is made of porous carbonaceous material, the negative electrode is made of zinc, the metal include zinc, the halogen includes chlorine, the electrolyte includes an aqueous zinc-chloride electrolyte, and the halogen reactant includes a chlorine reactant. One effect of this arrangement is generation of an electrical potential.

The basic operation of this embodiment is as follows: aqueous electrolyte is sucked up from a reservoir and through a mixing venturi where halogen such as elemental chlorine is metered into an electrolyte. The halogen mixes with and dissolves into the electrolyte while its latent heat of liquefaction also cools the mixture. The cooled and halogenated aqueous electrolyte passes through the pump and is delivered to positive electrodes in a stack assembly. The positive electrodes preferably are made of porous carbonaceous material such as porous graphite-chlorine. The electrolyte passes through the positive electrodes, reducing the dissolved halogen. The halogen-ion rich electrolyte then passes by one or more a negative electrode preferably made of a metal such as zinc, where electrode dissolution occurs. These reactions yield power from the electrode stack terminals and metal-halogen is formed in the electrolyte by reaction of the metal and the halogen.

FIG. 1 shows an electrochemical energy system housed in containment vessel 11 designed to achieve the foregoing. The system in FIG. 2 includes two basic parts: stack assembly 12 and reservoir 19, as shown in FIG. 1.

Stack assembly 12 is made up of a plurality of cells or cell assemblies 13 that include at least one positive porous electrode and at least one negative metal electrode. The cells preferably are stacked vertically. Pressurized halogen reactant is supplied via feed pipe 15 from a source external to the system through metering valve 17 to mixing venturi 18. Circulation pump 16 circulates the electrolyte from reservoir 19 through mixing venturi 18, through stack assembly 12, and back to reservoir 19 through a return pipe. It should be noted that some halogen reactant could be left in the electrolyte when it returns back to the reservoir from the cell.

In a preferred embodiment, the porous electrodes include carbonaceous material, the metal includes zinc, the metal electrode includes zinc, the halogen includes chlorine, the electrolyte includes an aqueous zinc-chloride electrolyte, and the halogen reactant includes a chlorine reactant.

Alternatively, different types of positive and/or negative electrodes can be used. In addition, the halogen reactant can be supplied from an internal source instead of or in addition to an external source. Furthermore, the mixing venture can be replaced with a different type of mixing element, and the metering valve can be replaced with a different type of metering element such as a positive displacement pump.

In a preferred embodiment, this arrangement results in cells that each has an electrical potential of two volts, giving a stack arrangement with 21 cells a potential of 42 volts. An enthalpy of expansion of the halogen from the external source preferably cools the system. Thus, a strong potential can be provided without generating excessive heat.

Electrolyte Flows

FIG. 2 illustrates flow paths of an electrolyte through the cell plates of an embodiment of the system illustrated in FIG. 1. In this figure, the electrolyte flow paths 28 are represented by arrows. These paths are from feed manifold 21, to distribution zone 22, through porous electrodes 23, over metal electrodes 25, to collection zone 26, through return manifold 27, and to return pipe 29. The electrolyte preferably is conveyed by the circulation pump from the reservoir to these paths and returns from these paths to the reservoir. One feature of these paths is that the return manifold preferably is upward-flowing return manifold, which can facilitate purging of gas from the cell during electrolyte flow.

In a preferred embodiment, membranes 24 on a bottom of metal electrodes 25 screen the flows of electrolyte from contacting the metal electrodes before passing through the porous electrodes. These membranes preferably are plastic membranes secured to bottoms of the metal electrodes with adhesive. Other types of membranes secured in other ways also can be used. Alternatively, the membranes could be omitted.

With the arrangement shown in FIG. 2, the porous electrode and the metal electrode in each cell are arranged to maintain contact with a pool of electrolyte in each cell when electrolyte flow stops and the feed manifold, distribution zone, collection zone, and return manifold drain.

Furthermore, the vertically stacked cells and the geometry of the cells result in flow paths of the electrolyte within each of the plural cells that tend to interrupt shunt currents that otherwise would occur when electrolyte flow stops. These shunt currents are not desired because they can lead to reactions between the plates that corrode the metal plates without generating any usable potential.

Before being conveyed through the porous electrode, the electrolyte mixed with the halogen reactant preferably undergoes concurrent first, second, and third order splits to provide a same flow resistance for different paths to the porous electrode. In this context, “concurrent” indicates that splits are aligned with other splits of the same order. Each split preferably divides the flow by two, although this need not be the case. FIG. 3 illustrates one possible cell design that can achieve these splits.

Cell Frames

FIG. 3 illustrates a cell design that uses cell frames to achieve the structures and flows shown in FIG. 2. These cell frames preferably include feed manifold element 31, distribution channels 32, flow splitting nodes 33, spacer ledge 35, flow merging nodes 36, collection channels 37, return manifold element 38, and bypass conduit elements 34.

When these cell frames are stacked vertically with the electrodes in place, these elements combine to form the elements shown in FIG. 2 as follows:

-   -   the feed manifold element in each of the plural cells frames         aligns with the feed manifold element in another of the cell         frames, thereby forming a feed manifold;     -   the distribution channels and the flow splitting nodes in each         of the cell frames align with the distribution channels and the         flow splitting nodes in another of the cell frames, thereby         forming a distribution zone;     -   the porous electrode for each cell sits above or below the metal         electrode for each cell on the spaces ledges of the cell frames,         thereby forming alternating layers of porous electrodes and         metal electrodes;     -   the flow merging nodes and the collection channels in each of         the plural cells frames align with the flow merging nodes and         the collection channels in another of the cell frames, thereby         forming a collection zone;     -   the return manifold element in each of the cell frames aligns         with the return manifold element in another of the cell frames,         thereby forming a return manifold; and     -   the bypass conduit elements in each of the cell frames align         with the bypass conduit elements in another of the cell frames,         thereby forming bypass conduits for fluid flow, a return pipe,         and/or electrical wires or cables.

The cell frames preferably are circular to facilitate insertion of the plural cells into a pressure containment vessel such as vessel 11. In a preferred embodiment, each of the cell frames also provides a pass-through for an alignment and clamping element to align and to hold the cell frames together.

The cell frame based design facilitates low-loss electrolyte flow with uniform distribution, bipolar electrical design, ease of manufacture, internal bypass paths, and elements by which the operational stasis mode (described below) can be achieved. Innovations of the cell frame include, but are not limited to, the flow-splitting design in the distribution zone that include first, second, and third order splits in the flow channels to deliver eight feed channels per cell to the reaction zone. This design attempts to ensure that each outlet to the reaction zone passes through the same length of channels, the same number and radius of bends, with laminar flow throughout and uniform laminar flow prior to each split. The design encourages division of flow volume equally, independent of flow velocity, uniformity of viscosity, or uniformity of density in the electrolyte. These features have been found to be of particular importance when a mixture of gaseous and liquid phases is fed through the system.

Alternatively, the same types of structures and flows (i.e., those shown in FIG. 2) can be achieved without using cell frames.

Modes of Operation

The energy cell system according to the invention preferably Cell has three modes of operation: Off Mode, Power Mode, and Stasis Mode. These modes are described below in the context of a zinc-chlorine system. However, the modes also can be implemented using other metal-halogen systems.

Off Mode is typically used for storage or transportation. During Off Mode, the circulation pump is off. A small amount of elemental chlorine in the stack assembly is reduced and combined with zinc ions to form zinc-chloride. The stack terminals preferably are connected via a shorting resistor, yielding a stack potential of zero volts. A blocking diode preferably is used to help inhibit reverse current flow through the system via any external voltage sources.

During Power Mode the electrolyte circulation pump is engaged. The catholyte (i.e., electrolyte) containing dissolved chlorine is circulated through the stack assembly containing the zinc anode plates. Electrons are released as zinc ions are formed and captured as chlorine ions are formed, preferably with an electrical potential of 2.02 volts per cell, thereby creating electrical power from the terminals of the collector plates preferably located at each end of the stack assembly. The demand for power from the system consumes chlorine and reduces pressure within the reservoir, causing the metering valve to release higher-pressure chlorine into the mixing venturi. This design feature aids both in speeding the dissolving of chlorine gas into the electrolyte, and uniformly cooling the electrolyte without risk of freezing at the injection point. The injection rate preferably is determined by the electrochemical reaction rates within the stack assembly. The metering valve and the circulation pump preferably provide sufficient response speed to match rapidly changing instantaneous power demands. As the compressed chlorine is released into the system, its enthalpy of expansion should absorb sufficient heat to maintain the energy cell within thermal operating limits.

During Stasis or Standby Mode, there should be little or no electrolyte flow or chlorine injection. The availability of the system preferably is maintained via a balancing voltage that is applied to maintain system availability. This balancing voltage tends to prevent self-discharge by maintaining a precise electrical potential on the cell stack to counteract the electrochemical reaction forces that can arise with the circulation pump off, thereby inhibiting electrochemical reactions and maintaining system availability.

The particular design of the cell plates tends to interrupt shunt currents that would otherwise flow through the feed and return manifolds, while maintaining cell-to-cell electrical continuity through the bipolar electrode plates.

While these are preferred modes of operation, the invention is not limited to these modes or to the details of these modes. Rather, some embodiments might have some of these modes, none of these modes, or different modes of operation.

Generality of Invention

This application should be read in the most general possible form. This includes, without limitation, the following:

-   -   References to specific techniques include alternative and more         general techniques, especially when discussing aspects of the         invention, or how the invention might be made or used.     -   References to “preferred” techniques generally mean that the         inventor contemplates using those techniques, and thinks they         are best for the intended application. This does not exclude         other techniques for the invention, and does not mean that those         techniques are necessarily essential or would be preferred in         all circumstances.     -   References to contemplated causes and effects for some         implementations do not preclude other causes or effects that         might occur in other implementations.     -   References to reasons for using particular techniques do not         preclude other reasons or techniques, even if completely         contrary, where circumstances would indicate that the stated         reasons or techniques are not as applicable.

Furthermore, the invention is in no way limited to the specifics of any particular embodiments and examples disclosed herein. Many other variations are possible which remain within the content, scope and spirit of the invention, and these variations would become clear to those skilled in the art after perusal of this application. 

1. A metal halogen electrochemical energy system whereby an electrical potential is generated, comprising at least one cell that includes: at least one positive electrode; at least one negative electrode; a reaction zone between the positive electrode and the negative electrode; at least one electrolyte that includes a metal and a halogen; and a circulation pump that conveys the electrolyte through the reaction zone, wherein the electrolyte and a halogen reactant are mixed before, at, or after the pump.
 2. A system as in claim 1, wherein the positive electrode comprises porous carbonaceous material.
 3. A system as in claim 1, wherein the negative electrode comprises zinc, the metal comprises zinc, the halogen comprises chlorine, the electrolyte comprises an aqueous zinc-chloride electrolyte, and the halogen reactant comprises a chlorine reactant.
 4. A system as in claim 1, further comprising a mixing venture that mixes the electrolyte and the halogen reactant.
 5. A system as in claim 1, wherein before being conveyed through the reaction zone, a flow of the electrolyte undergoes concurrent first, second, and third order binary splits to provide a same flow resistance for different paths to the reaction zone.
 6. A system as in claim 1, further comprising a reservoir from which the electrolyte is conveyed by the circulation pump to the cell and to which the electrolyte returns from the cell.
 7. A system as in claim 6, further comprising an upward-flowing electrolyte return manifold to facilitate purging of gas from the cell.
 8. A system as in claim 6, further comprising a return pipe through which the electrolyte returns from the cell to the reservoir.
 9. A system as in claim 6, wherein the halogen reactant is supplied from an external source.
 10. A system as in claim 6, wherein the halogen reactant is supplied under pressure, and wherein an enthalpy of expansion of the halogen from the external source acts to cool the system.
 11. A system as in claim 1, further comprising a metering valve or positive displacement pump that controls flow of the halogen reactant.
 12. A system as in claim 1, further comprising plural such cells.
 13. A system as in claim 12, wherein plural horizontal such cells are stacked vertically in the system.
 14. A system as in claim 12, wherein the plural cells further comprise plural cell frames.
 15. A system as in claim 14, wherein the cell frames are circular to facilitate insertion of the plural cells into a pressure containment vessel.
 16. A system as in claim 14, further comprising the pressure containment vessel.
 17. A system as in claim 14, wherein each of the cell frames further comprises a feed manifold element, distribution channels, flow splitting nodes, spacer ledges, flow merging nodes, collection channels, and a return manifold element.
 18. A system as in claim 17, wherein the feed manifold element in each of the plural cells frames aligns with the feed manifold element in another of the cell frames, thereby forming a feed manifold; the distribution channels and the flow splitting nodes in each of the cell frames align with the distribution channels and the flow splitting nodes in another of the cell frames, thereby forming a distribution zone; the positive electrode for each cell sits above or below the negative electrode for each cell on the spaces ledges of the cell frames, thereby forming alternating layers of positive electrodes and negative electrodes; the flow merging nodes and the collection channels in each of the plural cells frames align with the flow merging nodes and the collection channels in another of the cell frames, thereby forming a collection zone; and the return manifold element in each of the cell frames aligns with the return manifold element in another of the cell frames, thereby forming a return manifold.
 19. A system as in claim 17, wherein each of the cell frames further comprise bypass conduit elements for fluid flow and electrical wires or cables.
 20. A system as in claim 17, wherein each of the cell frames further provides a pass-through for an alignment and clamping element to align and to hold the cell frames together, and further comprises the alignment and clamping element.
 21. A system as in claim 12, wherein vertical steps in cell geometry result in interrupted electrolyte flow paths within each of the plural cells, thereby interrupting shunt currents that otherwise would continue to occur after electrolyte flow stops.
 22. A system as in claim 12, further comprising: a feed manifold and a distribution zone for the electrolyte to the plural cells; a collection zone and a return manifold for the electrolyte from the plural cells.
 23. A system as in claim 22, wherein the positive electrode and the negative electrode in each cell are arranged to maintain contact with a pool of electrolyte in each cell when electrolyte flow stops and the feed manifold, distribution zone, collection zone, and return manifold drain.
 24. A system as in claim 22, further comprising a reservoir from which the electrolyte is conveyed by the circulation pump to the feed manifold and to which the electrolyte returns from the return manifold.
 25. A system as in claim 24, further comprising an upward-flowing electrolyte return manifold to facilitate purging of gas from the cell.
 26. A system as in claim 24, further comprising a return pipe that is internal to the cell frames through which the electrolyte returns from the cell to the reservoir.
 27. A metal halogen electrochemical energy cell system, comprising at least one cell that includes a positive electrode, a negative electrode, a reaction zone between the positive electrode and the negative electrode, and flow distribution zones; an aqueous electrolyte that includes the metal and the halogen; a reservoir where the electrolyte is collected; and a circulation pump that conveys the electrolyte through the system; wherein the flow distribution zones contain flow-splitting nodes in which flow channels are concurrently and repeatedly divided in two to provide a same flow resistance for different paths to the reaction zone.
 28. A system as in claim 27, wherein the negative electrode comprises zinc, the halogen comprises chlorine, the positive electrode comprises porous carbonaceous material, the electrolyte comprises an aqueous zinc-chloride electrolyte, and the halogen reactant comprises a chlorine reactant.
 29. A metal halogen electrochemical energy cell system, comprising at least one cell that includes a positive electrode, a negative electrode, and a reaction zone between the positive electrode and the negative electrode; an aqueous electrolyte that includes the metal and the halogen; a reservoir where the electrolyte is collected; a circulation pump that conveys the electrolyte through the system; and a halogen metering element by which the halogen is replenished from an external source.
 30. A system as in claim 29, wherein the negative electrode comprises zinc, the metal comprises zinc, the halogen comprises chlorine, the positive electrode comprises carbonaceous material, the electrolyte comprises an aqueous zinc-chloride electrolyte, and the halogen reactant comprises a chlorine reactant.
 31. A system as in claim 29, wherein the halogen metering element is a valve or a positive displacement pump.
 32. A system as in claim 29, wherein chlorine is fed to the halogen metering element from the external source.
 33. A system as in claim 29, wherein an enthalpy of expansion of the halogen from the external source cools the system.
 34. A metal halogen electrochemical energy cell system, comprising at least one cell that includes a positive electrode, a negative electrode, and a reaction zone between the positive electrode and the negative electrode; an aqueous electrolyte that includes a metal and a halogen; a reservoir where the electrolyte is collected; and a circulation pump that conveys the electrolyte through the system; wherein a balancing voltage is applied to inhibit electrochemical reactions and thereby maintain system availability when the system is in a standby or stasis mode.
 35. A system as in claim 34, wherein the negative electrode comprises zinc, the halogen comprises chlorine, the positive electrode comprises carbonaceous material, the electrolyte comprises an aqueous zinc-chloride electrolyte, and the halogen reactant comprises a chlorine reactant.
 36. A metal halogen electrochemical energy cell system, comprising at least one cell that includes a positive electrode, a negative electrode, and a reaction zone between the positive electrode and the negative electrode; an aqueous electrolyte that includes the metal and the halogen; a halogen reactant that is mixed with the electrolyte; a reservoir where the electrolyte is collected; a circulation pump that conveys the electrolyte through the system; output terminals connected to at least the cell; and a blocking diode that is applied to the output terminals to inhibit reverse current flow within the system.
 37. A system as in claim 36, wherein the negative electrode comprises zinc, the metal comprises zinc, the halogen comprises chlorine, the positive electrode comprises carbonaceous material, the electrolyte comprises an aqueous zinc-chloride electrolyte, and the halogen reactant comprises a chlorine reactant.
 38. A method of generating an electrical potential using a metal halogen electrochemical energy system, comprising the steps of: mixing an electrolyte with a halogen reactant, with the electrolyte including a metal and a halogen; and conveying the electrolyte through at least one cell that includes at least one positive electrode and at least one negative electrode, wherein the electrolyte passes through the positive electrode and across the negative electrode.
 39. A method as in claim 38, wherein the positive electrode comprises porous carbonaceous material.
 40. A method as in claim 38, wherein the negative electrode comprises zinc, the metal comprises zinc, the halogen comprises chlorine, the electrolyte comprises an aqueous zinc-chloride electrolyte, and the halogen reactant comprises a chlorine reactant.
 41. A method as in claim 38, wherein the electrolyte and the halogen reactant are mixed by a mixing venturi.
 42. A method as in claim 38, further comprising the step of subjecting a flow of the electrolyte to concurrent first, second, and third order splits before being conveyed through the positive electrode, thereby providing a same flow resistance for different paths to a reaction zone between the positive electrode and the negative electrode.
 43. A method as in claim 38, wherein the electrolyte is circulated from a reservoir to the cell and returns from the cell to the reservoir.
 44. A method as in claim 43, further comprising the step of upward-flowing the electrolyte in a return manifold to facilitate purging gas from the cell.
 45. A method as in claim 43, further comprising the step of returning the electrolyte to the reservoir through a pipe.
 46. A method as in claim 43, further comprising the step of supplying the halogen reactant to the system from an external source.
 47. A method as in claim 43, wherein an enthalpy of expansion of the halogen from the external source acts to cool the system.
 48. A method as in claim 38, further comprising the step of controlling flow of the halogen reactant using a metering valve or positive displacement pump.
 49. A method as in claim 38, wherein conveying the electrolyte through at least one cell further comprises conveying the electrolyte through plural such cells.
 50. A method as in claim 49, wherein the plural horizontal cells are stacked vertically in the system.
 51. A method as in claim 49, wherein the plural cells further comprise plural cell frames.
 52. A method as in claim 51, wherein the cell frames are circular to facilitate insertion of the plural cells into a pressure containment vessel.
 53. A method as in claim 51, wherein the plural cells are contained in a pressure containment vessel.
 54. A method as in claim 51, wherein conveying the electrolyte through the plural cell frames further comprises conveying the electrolyte through a feed manifold element, distribution channels, flow splitting nodes, spacer ledges, flow merging nodes, collection channels, and a return manifold element.
 55. A method as in claim 54, wherein the feed manifold element in each of the plural cells frames aligns with the feed manifold element in another of the cell frames, thereby forming a feed manifold; the distribution channels and the flow splitting nodes in each of the cell frames align with the distribution channels and the flow splitting nodes in another of the cell frames, thereby forming a distribution zone; the positive electrode for each cell sits above or below the negative electrode for each cell on the spaces ledges of the cell frames, thereby forming alternating layers of positive electrodes and negative electrodes; the flow merging nodes and the collection channels in each of the plural cells frames align with the flow merging nodes and the collection channels in another of the cell frames, thereby forming a collection zone; and the return manifold element in each of the cell frames aligns with the return manifold element in another of the cell frames, thereby forming a return manifold.
 56. A method as in claim 54, wherein each of the cell frames further comprise bypass conduit elements for fluid flow and electrical wires or cables.
 57. A method as in claim 54, wherein each of the cell frames further provides a pass-through for an alignment and clamping element to align and to hold the cell frames together, and further comprises the alignment and clamping element.
 58. A method as in claim 49, further comprising the step of using vertical steps in cell geometry to interrupt flow paths of the electrolyte within each of the plural cells to interrupt shunt currents that otherwise would continue to occur after electrolyte flow stops.
 59. A method as in claim 49, wherein conveying the electrolyte through the plural cells further comprises conveying the electrolyte through a feed manifold and a distribution zone to the plural cells and through a collection zone and a return manifold from the plural cells.
 60. A method as in claim 59, further comprising the step of maintaining contact with a pool of electrolyte in each cell when electrolyte flow stops and the feed manifold, distribution zone, collection zone, and return manifold drain.
 61. A method as in claim 59, wherein conveying the electrolyte through the plural cells further comprises conveying the electrolyte from a reservoir to the feed manifold and from the return manifold to the reservoir.
 62. A method as in claim 61, further comprising the step of upward-flowing electrolyte in the return manifold to facilitate purging gas from the cell.
 63. A method as in claim 61, further comprising the step of returning the electrolyte to the reservoir through a pipe that is internal to the cell frames.
 64. A method of generating an electrical potential using a metal halogen electrochemical energy system, comprising the steps of: conveying an aqueous electrolyte that includes the metal and the halogen through at least one cell that includes a positive electrode, a negative electrode, a reaction zone between the positive electrode and the negative electrode, and flow distribution zones; and collecting the electrolyte in a reservoir; wherein the flow distribution zones contain flow-splitting nodes in which flow channels are concurrently and repeatedly divided in two to provide a same flow resistance for different paths to the reaction zone.
 65. A method as in claim 64, wherein the negative electrode comprises zinc, the metal comprises zinc, the halogen comprises chlorine, the positive electrode comprises carbonaceous material, the electrolyte comprises an aqueous zinc-chloride electrolyte, and the halogen reactant comprises a chlorine reactant.
 66. A method of generating an electrical potential using a metal halogen electrochemical energy system, comprising the steps of: conveying an aqueous electrolyte that includes the metal and the halogen through at least one cell that includes a positive electrode, a negative electrode, and a reaction zone between the positive electrode and the negative electrode; collecting the electrolyte in a reservoir; and replenishing the halogen from an external source using a halogen metering element.
 67. A method as in claim 66, wherein the negative electrode comprises zinc, the metal comprises zinc, the halogen comprises chlorine, the positive electrode comprises carbonaceous material, the electrolyte comprises an aqueous zinc-chloride electrolyte, and the halogen reactant comprises a chlorine reactant.
 68. A method as in claim 66, wherein the halogen metering element is a valve or positive displacement pump.
 69. A method as in claim 66, wherein chlorine is fed to the halogen metering element from the external source.
 70. A method as in claim 66, wherein an enthalpy of expansion of the halogen from the external source acts to cools the system.
 71. A method of generating an electrical potential using a metal halogen electrochemical energy system, comprising the steps of: conveying an aqueous electrolyte that includes a metal and a halogen through at least one cell that includes a positive electrode, a negative electrode, and a reaction zone between the positive electrode and the negative electrode; collecting the electrolyte in a reservoir; and applying a balancing voltage to inhibit electrochemical reactions and thereby maintain system availability when the system is in a standby or stasis mode.
 72. A method as in claim 71, wherein the negative electrode comprises zinc, the metal comprises zinc, the halogen comprises chlorine, the positive electrode comprises carbonaceous material, the electrolyte comprises an aqueous zinc-chloride electrolyte, and the halogen reactant comprises a chlorine reactant.
 73. A method of generating an electrical potential using a metal halogen electrochemical energy cell system, comprising the steps of: conveying an aqueous electrolyte that includes a metal and a halogen through at least one cell that includes a positive electrode, a negative electrode, and a reaction zone between the positive electrode and the negative electrode; mixing a halogen reactant with the electrolyte; collecting the electrolyte in a reservoir; and applying a blocking diode to output terminals of the system to inhibit reverse current flow within the system.
 74. A method as in claim 73, wherein the negative electrode comprises zinc, the metal comprises zinc, the halogen comprises chlorine, the positive electrode comprises carbonaceous material, the electrolyte comprises an aqueous zinc-chloride electrolyte, and the halogen reactant comprises a chlorine reactant. 